1. Field of the Invention
The present invention relates to an image forming apparatus having an image bearing member such as a photoconductor, a transfer roller which transfers an image on the image bearing member to a transfer member through a transfer nip between the image bearing member and the transfer roller, and a discharger which discharges the transfer member after the image has been transferred thereto.
2. Description of the Background Art
An image forming apparatus is known which has a transfer roller for transferring an image on an image bearing member to a transfer member through a transfer nip formed between the image bearing member and the transfer roller.
In such an image forming apparatus, as illustrated in FIG. 6, a drum-like photoconductor 51 as the image bearing member is rotated at a prescribed angular velocity in a direction indicated by an arrow C. An outer surface of the photoconductor 51 is charged uniformly to have a prescribed potential by a charger 52. Then, the charged surface is irradiated with light L by an exposure device (not shown) so that an electrostatic latent image is formed on the photoconductor 51.
The electrostatic latent image is developed with toner by a developer 54 so that a toner image is formed thereon. The toner image is carried with the rotation of the photoconductor 51 indicated by the arrow C, to a transferring region where a transfer roller 55 is disposed.
Further, a transfer sheet of paper (transfer member) P is fed by a sheet supplying member (not shown) at a prescribed timing. The toner image is transferred to the transfer sheet P using the transfer roller 55. Then, the transfer sheet P is fed out to a discharged sheet receiving tray etc., via a fixing device 56.
As shown in FIG. 7, the transfer roller 55, which is brought into contact with the outer surface of the photoconductor 51, generally includes a metal shaft 55a and a conductive elastic layer 55b made of conductive rubber or the like. The conductive elastic layer 55b is formed so that the metal shaft 55a except for both ends thereof is covered with the conductive elastic layer 55b. The both ends of the metal shaft 55a are left uncovered.
The metal shaft 55a is disposed so that the axis thereof is disposed parallel to that of the photoconductor 51. Both ends of the metal shaft 55a are rotatably supported by a plurality of bearings, respectively. The conductive elastic layer 55b is configured to be brought into contact with the outer surface of the photoconductor 51, imposing a prescribed pressure thereon. The transfer roller 55 is rotated at substantially the same circumferential speed as the photoconductor 51, and is biased by an electric source to have a bias potential opposite to that of the toner image on the photoconductor 51. Thereby, the transfer sheet P which is fed into the transfer nip is electrostatically charged so that the toner image is transferred from the photoconductor to the transfer sheet P.
As described above, the surface of the transfer roller 55 is generally made of a conductive elastic layer 55b which is compressed in the transfer nip where the conductive elastic layer 55b is brought into contact with the photoconductor 51 or the transfer sheet P. The compression of the compressed elastic conductive layer 55b in the transfer nip is released after the compressed portion has passed through the transfer nip. Because the compression and the release of compression of the conductive elastic layer 55b are repeated many times, the conductive elastic layer 55b is remarkably deteriorated by fatigue thereof. Therefore, a lifetime of the transfer roller 55 is generally shorter than that of the other components or the image forming apparatus.
Accordingly, replacement operations of a deteriorated transfer roller are generally required several times during the total lifetime of an image forming apparatus. In such an image forming apparatus, the transfer roller is configured so as to be attachable to and detachable from the main body of the image forming apparatus.
Because a transfer roller is a consumable component, many background image forming apparatuses are devised so that a transfer roller is easily detached from and attached to an image forming apparatus, in order to perform the replacement operation efficiently.
For example, an image forming apparatus disclosed in Japanese Laid-Open Patent Publication No. 6-3978 includes a transfer unit having a transfer roller and a supporting member for supporting the transfer roller. The transfer unit is configured to be detachable from and attachable to the image forming apparatus. The transfer unit may further include a pin-discharger for discharging a transfer member after an image has been transferred thereto. Thereby, the pin-discharger, as well as the transfer roller, can be replaced at once.
However, when the above-mentioned transfer unit is detached from the image forming apparatus, other components such as a plurality of bearings for rotatably supporting the transfer roller, a plurality of spring for pressing the plurality of bearings against the photoconductor, the pin-discharger if any, and so forth, are also taken out integrally, which may not need to be replaced. This is wasteful and contradicts the current trend toward reduction of wastes.
Further, as shown in FIG. 8, the transfer unit includes a transfer roller 65, a supporting member 63, a plurality of springs 67, a conductive bearing 61, a non-conductive bearing 62, and a plurality of stoppers 68. The combination of bearings 61 and 62 support the metal shaft 65a of the transfer roller 65. The combination of bearings 62 and 63 are each capable of being slid in a direction in which the plurality of springs 67 respectively press the combination of bearings 61 and 62. The plurality of stoppers 68 limit the movable range of the transfer roller 65, and thereby prevent the transfer roller 65 from falling off the combination of bearings 61 and 62.
Accordingly, in the process of taking out only the transfer roller 65 from the transfer unit, the plurality of stoppers 68 must be kept deformed by a force greater than a prescribed force, which is generally applied thereto using a jig or the like. Then, the transfer roller 65, as gripped by an operator's hand, can be drawn out from the transfer unit. Therefore, the job of taking out the transfer roller 65 is troublesome.
In addition, there may be a risk of dropping the transfer roller 65 during the process of taking it out, or injury caused by accident when the plurality of stoppers 68 are kept deformed using the jig.
Another background image forming apparatus is disclosed in Japanese Laid-Open Patent Publication No. 6-64279, which includes a cleaning tool having a handle. A brush is provided on one end of the handle, and a hooking portion that fits to a metal shaft of a transfer roller is provided on the other end. The transfer roller is configured to be easily taken out using the cleaning tool.
However, the cleaning member is not a necessary component for the transfer unit, although the hooking portion is provided for the operation of taking out the transfer member. Therefore, the problem is that the cost is increased by the cleaning member.
Further, in order to improve separation properties of the pin as an electrode for discharging the transfer member after an image has been transferred thereto, the end of the pin-discharger may be disposed close to the transfer nip, in which the transfer roller and the photoconductor are brought into contact with each other. In this case, however, the pin-discharger which is disposed close to the transfer roller is an obstacle in the operation of taking out the transfer roller.